ALUMINA. 



371 



Fig. 388. 



Fig- 387. Fig. 387. The angles of the crystal are 



about 119°. 



Near the banks of Muscolunge lake, in 

 the town of Alexandria, this mineral is found 

 in small but regular and perfect six-sided 

 tables of a dark brown colour, in white lime- 

 stone. Fig. 388. M or M' on A 120°. 

 The plumose variety of mica has also 

 been found associated with spinelle in white limestone, near the village of Oxbow. 



New-York County. The dolomite at Kingsbridge, and elsewhere, contains mica, which 

 is sometimes in the form of perfect six-sided tables. It exhibits a variety of colours. The 

 plates are seldom of large size. 



Orange County. Mica of almost every variety of colour and form occurs in this county. 

 Many of the localities are of great interest. One of these perhaps most deserving of notice, 

 is on the bank of a stream running from Mount Basha pond, near Forshee's iron mine, in the 

 town of Monroe. The mica is in augite rock, or rather in a bed of this mineral, with scattering 

 crystals of quartz contained in gneiss. The plates interlace each other in various directions, 

 and some of them are of large size. Dr. Horton and myself obtained a specimen, now in the 

 State Cabinet, which is twenty-two inches in diameter ; but plates of nearly three feet in 

 diameter have been observed at the locality. They are, however, usually fractured by the 

 agency of water and frost, so as to prevent their removal in an entire form. The colour of 

 this mica is greenish, and it breaks into rhomboidal fragments.* 



At the Wilks or Clove mine, in the vicinity of the preceding, plates of mica of a blackish 

 green colour, and from one to five inches in length, are found associated with the magnetic 

 iron ore. 



Near Greenwood furnace, mica occurs in black or greenish black crystals, which are some- 

 times six or seven inches in diameter. It is associated with 

 crystallized pyroxene, coccolite and calcareous spar. The 

 most common form is an oblique rhombic prism. Fig. 389, 

 a on a' usually about 120° ; P on a 114° to 115°. 

 There is also a regular six-sided prism, the sides inclining to each other at an angle of 120° ; 

 but in these, as in the preceding, the inclination of the terminal to the lateral planes is about 

 114° or 115°, and 65° or 66°. Figs. 390, 391 and 392 represent sections of various forms 



Fig. 391. 



Fig. 392. 



* The mica at this locality seems to be sufficiently abundant for profitable exploration. 



